Manufacture of lignin derivatives



April 26, 1960 J. l.. GARDON ETAL 2,934,531

MANuFAcTuRE oF LIGNIN DERIvATrvE-s Filed Deo. 2, 1957 INVENTORS JOHN. l.. GARDO o BENGT LEOPOLD By Akt rates MANUFACTURE F LIGNIN DERIVATIVES John L. Gardon and Bengt Leopold, Hawkesbury, 0n-

tario, Canada, assignors to Canadian International Paper Company, Montreal, Quebec, Canada, a corporation of Canada Application December 2, 1957, Serial No. 699,997

2 Claims. (Cl. 260-124) as phenols or aldehydes.

It is generally known that when solid lime is added to sulphite waste liquor at temperatures lower than 100 C. a precipitate is obtained consisting of lime and basic calcium ligninsulphonates. In this type of precipitation the lignin sulphonates do not suffer any appreciable structural changes but retain their polar hydrophilic nature.

It is also known that when lignin sulphonates are heated with alkaline reagents at temperatures up to 200 C., sulphonic acid groups are split off, 4and consequently theVv lignin becomes more hydrophobic. Such lignin products have been suggested for the use as extenders or substitutes for thermosetting resins and adhesives. However, such lignin products all suffer from the disadvantage of low reactivity and poor quality of the cured resin, and can normally only be converted to acceptable resins by the addition of substantial amounts of chemicals such as phenols and/or aldehydes.

We have discovered that when neutral or basic lignin sulphonate salts are heated to temperatures in the range of V220 to 350 C., but preferably from 250 to 290 C., at substantially atmospheric pressure in the presence of an excess of lime or other solid alkaline agents and in extent, as shown by its solubility in alcohol and other4 polar solvents. On heating the product cures very rapidly, without any additions, to form a strong, tough, waterresistant binder.

A further feature of this novel product is its high reducing power which may make it useful in certain applications where atmospheric oxidation is to be prevented.

A possible explanation of this unexpected result is the following:

Normally, desulphonated lignin contains a relatively small number of phenolic hydroxyl groups and carbonyl groups, and the possibilities of forming cross-links on heating are quite limited. The formation of a crosslinked resin can therefore only be achieved by the addition of a phenol and/or aldehyde, and the lignin acts essentially as an extender.

The product obtained according to the process of the present invention, on the other hand, contains a substantial number of carbonyl groups and phenolic hydroxyl groups and is thus capable of forming cross-links on heatarent G ing. It can be said that the lignin obtained according-.to

this process is similar to a' B stage phenol formaldehyde resin in its solubility and curing characteristics.

Accordingly, an object of this invention is to provide a novel process for obtaining highly reactive lignin products of high carbonyl and phenolic hydroxyl content in a solid-solid reaction under alkaline conditions.

A further object of this invention is to provide a process of the character stated which includes the step of heating a reaction mixture consisting of a lignin sulphonate salt and a solid alkaline reagent in the dry state to about 220 to 350 C. at atmospheric pressure.

A further object of this invention is to provide a process of the character stated which includes the steps of precipitating basic lignin sulphonate from waste sulphite liquor with an excess of a solid alkaline reagent, drying the precipitated basic lignin sulphonate, and then calcining it at atmospheric pressure to about 220 to 350 C.

A further object of this invention is to provide a process of the character stated in which the calcined lignin productV is de-ashed with an aqueous mineral acid.

A further object of this invention is to provide a process of the character stated in which the alkaline reagent is selected from the group consisting of the oxides, hydroxides and carbonates of alkaline earth metals.

This application is a continuation-in-part of our copending application Serial No. 619,430, led October 31, 1956, now abandoned.

The sole ligure in the drawing is a flow diagram by which the process of this invention may be practiced.

The starting materials for this dry state desulphonation consist of a dry lignin sulphonate preparation and a solid basic reagent. Suitable reaction mixtures can be prepared by either (l). filtering olf the product obtained by the precipitation of basic lignin sulphonates fromv waste sulphite liquor with an excess of solid lime under atmospheric pressure, or (2) mixing an excess of lime with the sulphite waste liquor and/or sulphite waste liquor concentrate and drying this mixture, or (3) mixing dried sulphite waste liquor solids with lime in the dry state, wetting the mixture uniformly to yield a paste and drying the same, or (4) mixing thoroughly any kind of neutral or alkaline lignin sulphonate salt preparation with any kind of solid alkaline reagent, eg., sodium hydroxide, potassium hydroxide, magnesium hydroxide, or magnesium oxide, to yield a dry reaction mixture, in a manner familiar to those versed in the ait.

We prefer to carry out the drying and the subsequent heat treatment of any of the aforementioned reaction mixtures in one stage, but these operations can also be carried out separately. We also prefer the use of a directly heated continuous rotary oven or kiln for this purpose, but any other kind of equipment can also be used in which the reaction mixture can be heated to the desired temperature.

After the calcination is completed, the ligneous matter in the reaction mixture may be freed from minerals (deashed) in aqueous suspension. For de-ashing we prefer to apply sulphurous acid and subsequently use the filtrate containing the lime as calcium bisulphite in the cooking acid for the acid pulping of wood, but other acids, such as hydrochloric acid, may also be used for de-ashing. After de-ashing the ligneous end-product is iltered and washed. The whole procedure is illustrated as a flow sheet in the single figure of the drawing.

The yield and the composition of the de-ashed ligneous end product depend primarily upon the highest temperature attained by the reaction mixture during the desulphonation reaction, less upon the time during which this temperature is maintained, and only to a limited extent upon the nature and amount of the alkaline desul- Patented Apr. 26, 1960 phonating agent, as long as this agent is present in excess to render the reaction mixture alkaline. Increasing reaction temperature increases the yields, carbonyl contents, phenolic hydroxyl contents, and decreases the sul- 4 the feed and 280 C. at the discharge end. After having passed through one-third of the length of the kiln the reaction mixture reached a temperature higher than that of the kiln wall, but the temperature did not exceed 300 C.

phur contents. Reaction temperatures higher than 350 5 at any point. C. however, lead to products insoluble in alcohol and 100 kg. of calcined material obtained under steady other polar solvents, possibly indicating that a cross-linkstate conditions was then suspended in 500 liters of ing has taken place. The yields, calculated on basis of water and 52 kg. of sulphur dioxide were stirred into the lignin sulphonates initially present in the reaction the suspension. The insoluble product was filtered, 'mixture and the quantity of de-ashed ligneous end- 10 washed with water and dried at 60 C. The resulting product obtained, may be as high as 85%. The sulphur end-product, when bone-dry, weighed 40 kg. and concontent -of the ligneous matter is generally reduced from tained 2.5% sulphur and 3.4% ash. the initial 5 to 7% to 1.8 to 3%. The ash content of the The dry, de-ashed ligneous end-product is. a brown de-ashed product may range from 2 to 6%. The pH of ifreeflowing powder. It is insoluble in aqueous mineral the de-ashed product dissolved in 60% aqueous alcohol 15 acids, neutral Water and non-Polar SolVentS Snell aS solution, or suspended in water, is between 2.5 and 4.5. ether, but soluble in aqueous alkaline solutions and in The carbonyl content can vary from 0.45 to 2.1 milpolar organic Solvents of IniXilfeS Snell aS dimethyl liequivalents per gram and the total hydroxy content formamide, formie acid and aqueous aleollolfrom 4.1 to 7.0 milliequivalents per gram. zo Example 3 Example 1 Saturating kraft paper was impregnated with a solu- A suspension of 2.8 kg. of calcium hydroxide in 5 tion of the lignin product obtained in Example 2 in 70% liters of Water was stirred at 75 C. into 75 liters of sulaqueous ethanol. The nal lignin content of the paper phite Waste liquor containing 10.5 kg. of solids. The was 42.5% by weight. The layers of such paper were resulting precipitate (6.1 kg.) was ltered and dried. pressed together at 150 C. and 1200 p.s.i. for 5 min- Portions of 2 kg. were then calcined at varying temutes. The resulting board had a modulus of rupture of peratures in a small gas-heated kiln provided with a 27,800 p.s.i., a modulus of elasticity of 1,400,000 p.s.i., stirrer for 11/2 hours. After calcination the reaction an internal bond of 487 p.s.i. and a water absorption of mixture was stirred with an excess of SO2 dissolved in 10.5% after 24 hours of soaking. water. The resulting solid was filtered oft, Washed with The pure de-ashed ligneous end-products may iind use water and dried. The properties of the products are as binders for hard boards, ber boards, or chip boards, shown in the following table. The products are all and as components in mounting compounds vand in adinsoluble in ether. hesives. The de-ashed end-product may be used as an Carbonyl Total Mcthoxyl Sulphur Reducing Solubility Content, Hydroxyl Content, Content, Groups, Caleination Temperature,C. in70% millicquiv- Content, milliequivmilliequvmilliequlvethanol, alents per m|lliequivalents/gm. alcnts/ alents of percent gram alents per gram glucose gram per gram Starting Material Nil 0. 1 4. 00 5. 70 1.84 1. 23 247 93. 5 o. 45 4. 1o 4. 84 0.73 1.50 280---- 96. s o. 88 4. 75 4. 02 1.10 1. so 300 94. 0 1. 57 e. 10 3. o5 0.87 3. 40

The carbonyl groups were determined using the hyextender in acidic adhesives and as a rubber ller. Aldroxylarnine method described by Eitel (I. Prakt. Chem. kaline solutions of the de-ashed end-product may rld use 159, 292 (1942)), and total hydroxyl groups by the as dispersants for clay, cement, carbon black, drilling acetylation method described by Freed and Wayne (Ind. mud used in oil wells, and other special purposes. The Eng. Chem. Anal. Ed. 8, 278 (1936)). un-deashed heat treated reaction mixture may be used as Attempts to determine phenolic hydroxyl groups led extender in alkaline adhesives. to Very unreliable results, but it seems obvious from the We claim: parallel increase in hydroxyl and decrease in methoxyl 1. In a process of obtaining highly reactive lignin that the majority of the newly formed hydroxy group reproducts of high carbonyl and phenolic hydroxyl content, sult from demethylation and are thus phenolic. the step of heating a reaction mixture consisting ofa Reducing groups were determined using a modified lignin sulphonate salt and a solid alkaline reagent in the Somogyi method, as described by Sundman, Saarnio and dry state at a temperature between 220 C. and 350 C. Gustafson (Paper and Timber 4a, 115 (1951)). 60 2. The process of obtaining highly reactive lignin products ofrhigh carbonyl and phenolic hydroxyl content Example 2 from waste sulphite liquor which comprises precipitating 32 kg. of calcium oxide was stirred at 60 C. into basic calcium lignin sulphonate from waste sulphite 300 liters of sulphite waste liquor containing 200 kg. of liqnol' With an eXCeSS of Solid lime at temperatures not Solids. The resulting precipitate was filtered, dried and exceeding 100 C., drying the precipitated basic calcium ground. The product was fed into a rotary kiln at a rate lignin sulphonate, and heating the basic calcium lignin of 15 kg. per hour. The speed of rotation 0f the kiln sulphonate at a temperature between 250 C. and 290 C. gdztlolrlirvttsiogbeo atlha irlnti References Cited in the le of this patent 1 thermocouples for measuring the temperaturep of the UNITED STATES PATENTS product and of the wall of the kiln at different points.' 1,298,477 Drewsen Mar. 25, 1919 The wall temperature of the kiln was held at 250 C. at 2,683,706 Muller July 13, 1954 

1. IN A PROCESS OF OBTAINING HIGHLY REACTIVE LIGNIN PRODUCTS OF HIGH CARBONYL AND PHENOLIC HYDROXYL CONTENT, THE STEP OF HEATING A REACTION MIXTURE CONSISTING OF A LIGNIN SULPHONATE SALT AND A SOLID ALKALINE REAGENT IN THE DRY STATE AT A TEMPERATURE BETWEEN 220* C. AND 350* C. 